Note: Descriptions are shown in the official language in which they were submitted.
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GREY GLASS COMPOSITION
AND METHOD OF MAKING SAME
FIELD OF THE INVENTION
This invention relates to grey glass compositions and
methods of making same. More particularly, this invention
relates to erbium-containing grey glass compositions having
low light transmittance in the UV and IR range while, at
the same time, having high light transmittance in the
visible range, thus making such glasses suitable for use as
windows and windshields in the automotive industry and
architectural field, as well as, in certain embodiments, as
eyeglass lenses.
BACKGROUND OF THE INVENTION
The automotive industry, for a number of years, has
centered on the color grey, sometimes referred to as
"neutral grey", as the aesthetic color of choice for
automotive windows. At the same time, this industry, as
well as the eyeglass art, have demanded that transmission
in the UV and IR range of the light spectrum be minimized.
This is also desirable at certain times in the
architectural field. Governmental regulations in the
automotive industry, moreover, simultaneously insist that
the visible light transmittance be at least 700 or greater
in certain, if not all, vehicular windows when provided by
the original equipment manufacturer of the vehicle (e.g.
GM, Ford, Chrysler etc., in the U.S.A.). A need is thereby
created in these diverse industries for a glass which
achieves these properties.
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A glass window, windshield or other glass article is
said to have the desirable color "grey", sometimes referred
to as "neutral grey", if it manifests a dominant wavelength
from about 435nm, and preferably from about 470nm, to less
than about 570nm, in combination with an excitation purity
of less than about 4.5a. This, then, defines the meaning
of the term "grey" as used herein. A still more preferred
range of dominant wavelength, thus defining a more
preferred "grey" as used herein, is about 480nm - 550nm,
and in like manner, a more preferred range of purity is
about 0.2 - 4.501. The appearance of such glass, thus
defined, has been found to be of a truly "grey" color,
rather than wandering into an objectionable hew of bronze,
green or purple, or some other color. This "grey" color,
as aforesaid, has found a unique demand in the automotive
market, but it also has potential utility in the
architectural and eyeglass markets as well.
At the same time that a true "grey" color is to be
achieved, there is the usually required need to achieve
rather strict levels of light transmission defined
conventionally by:
LTa as visible light transmi.ssion,
W as ultraviolet light transmission,
IR as infrared light transmission, and
Te as total solar transmission.
In order to specify the parameters of these
characteristics, it is generally necessary to specify the
thickness of the glass which is the subject of the
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measurement. As used herein, in this respect, the term "a
nominal thickness of about lmm - 6mm," and in certain
embodiments, "about 3mm - 4mm" means that the
characteristics of the glass are those experienced when the
thickness of the actual glass under investigation is
adjusted for that nominal thickness range. Such thickness
ranges, in this respect, are generally recognized as
conventional thicknesses for glass sheets made by the float
glass process, as well as a recognized thickness range for
the automotive industry.
When measured at the specified nominal thickness (e.g.
3.2mm or 4mm) the important characteristic of color
achieved by this invention may be reported by the
conventional CIE LAB technique (see U.S. Patent No.
5,308,805). Such a technique is reported in CIE
Publication 15.2 (1986) and ASTM: E 308-90 [Ill. C 2
observer].
"Luminous transmittance" (LTa) [2 observer] is a
characteristic and term well understood in the art, and is
used herein in accordance with its well known meaning [see
U.S. Patent No. 5,308,805]. This term is also known as
Ill. A visible transmittance (380 - 780 nanometers
inclusive), and its measurement is made in accordance with
CIE Publication 15.2 (2986) and ANSI test method Z26.1.
"Total solar energy transmittance" (T$) (300 - 2100nm
inclusive, integrated using Simpson's Rule at 50nm
intervals using Parry Moon Air Mass = 2) is another term
well understood in the art [see U.S. Patent 5,308,8051 . It
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is used herein according to this well known meaning. its
measurement is conventional and well known.
The terms, and characteristics, of "ultraviolet light
transmittance" (%UV), "infrared energy transmittance"
(oIR), "dominant wavelength" (DW) and "excitation purity"
(i.e. % purity", or Pe) are also well understood terms in
the art, as are their measurement techniques. Such terms
are used herein, in accordance with their well known
meaning [see U.S. Patent No. 5,308,805].
"Ultraviolet transmittance" (oUV) is measured herein
using Parry Moon Air Mass = 2 (300 - 400nm inclusive,
integrated using Simpson's Rule at lOnm intervals). Such
a measurement is well known in the art.
"Infrared transmittance" (oIR) is conventionally
measured using Simpson's Rule and Parry Moon Air Mass = 2
over the wavelength range 800 - 2100nm inclusive at 50nm
intervals. Such a measurement is well known in the art.
"Dominant wavelength" (DW) is calculated and measured
conventionally in accord with the aforesaid CIE Publication
15.2 (1986) and ASTM: E 308-90. Its calculation and
measurement are also well known in the art. As used
herein, therefore, the term "dominant wavelength" includes
both the actual measured wavelength and, where applicable,
its calculated complement.
"Excitation purity" (Pe or o"purity") is measured
conventionally in accord with CIE Publication 15.2 (1986)
and ASTM: E 308-90.
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For automotive windows (including windshields) it is
desirable that the glass have the following characteristics
(when measured at a nominal thickness of about 3mm - 4mm
and preferably at about either 3.2 mm or 4mm as the
particular situation may require), and often in the
ultimate product as well:
LTa, greater than about 70%
UV, less than about 42%, preferably less
than about 38%
IR, less than about 37%, preferably less
than about 28%
Te, less than about 47%.
Generally speaking, the prior art has at times been
able to meet these automotive requirements, including the
achievement of the necessary, aesthetic "grey" color by
using as the essential ingredients of the colorant portion
in an otherwise conventional silicate glass composition
(e.g. a typical soda-lime-silica float glass composition),
a combination of cobalt admixed with one or more of
selenium, nickel, and cerium, along with an essential
amount of iron. In many instances this combination was
thought critical to achieving both a grey color and the
requisite light transmission properties, or at least a
"neutral bronze color." See, for example, U.S. Patent Nos.
4,101,705; 5,061,659; 5,264,400; 5,318,931; 5,380,685; and
Japanese Patent JP4-280834.
Unfortunately, these prior art combinations often had
various problems associated with them. For example,
cerium, being a well known UV absorber when present in
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glass in its reduced form, Ce3+, should be avoided for the
following reason. Iron is conventionally introduced into
glass in the form of Fe2031 part of which should be reduced
to FeO to achieve the requisite low IR transmittance value.
Cerium, which is introduced into glass in the form of CeO2,
is known to oxidize divalent iron to trivalent iron either
directly or by competition with any reducing agent present
in the glass melt. Therefore, coexistence of iron oxide
and cerium oxide will inevitably lead to a decrease in the
concentration of FeO in the glass and thus will reduce its
IR absorbing power.
The use of nickel in these prior art compositions
presented the problem of nickel sulfide stones forming in
the ultimate product. Selenium, furthermore, is difficult
to retain in the glass during glass making. The loss of
selenium created a difficulty in controlling the redox
ratio in the glass, which ultimately adversely affected
transmittance values. Without some, or all, of these
aforesaid key ingredients, cobalt used by itself with the
iron as the colorant portion of the glass composition,
could not achieve the requisite combination of Lta and grey
color as defined above.
Several attempts in the past have been made to employ
the rare earth element erbium (reported conventionally as
Er203, and used herein according to this conventional
practice) as a colorant in automotive windows and other
glass articles. For example, the aforesaid U.S. Patent No.
5,264,400 reports the use of such an ingredient in glasses
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of both bronze and grey tinted colors. However, as
reported therein, the use of cerium oxide is an essential
ingredient in the composition.
As another example, the aforesaid Japanese Patent No.
280834 employs ErZ03 in a glass composition which is then
said to have a "low thermal expansion coefficient." The
glass employs from 10-20% B203 and thus is properly referred
to as a borosilicate glass, rather than the more
conventional soda-lime-silica glasses used in automotive
windows. While stating, in effect, that cobalt and nickel
are optional, and no use of Se or Ce is reported, the
dominant wavelength reported is accordingly rather high,
i.e. from 570 - 610nm, or tending toward an objectionable
bronze color, even at the lower wavelengths achieved,
rather than achieving a true "grey" color as defined above.
Reference to the examples presented in this Japanese
Patent '834, moreover, demonstrates that to achieve the
lower range of wavelengths (e.g. the lowest reported in
578nm) the total iron content had to be kept at a very low
0.25o and the excitation purity was a very high 14.2%.
This leads to the conclusion that this patent does not
achieve, nor does it teach how to achieve, a true "grey"
glass which, through the use of a high level of iron in the
colorant portion (rather than the low level of iron used),
also simultaneously achieves low UV and IR and high LTa
transmittances, along with a true "grey" color. Indeed, in
those examples which do not use cerium or some other W
absorber, and with the low levels of iron employed in those
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examples achieving lower dominant wavelengths, it is to be
presumed that unacceptably high IR and UV transmittance
values are the result.
In view of the above, it is apparent that there exists
a need in the art for a new glass composition which
overcomes the above problems while achieving the requisite
grey color and meets the other solar management
requirements of the particular industry in which it is to
be used. It is a purpose of this invention to fulfill this
and other needs in the art which will become more apparent
to the skilled artisan once given the following disclosure.
SUMMARY OF THE INVENTION
Generally speaking, this invention fulfills the above-
described needs in the art by providing a unique glass
composition, glass articles made therefrom, and a unique
method of making the glass. In this respect, the unique
glass compositions are comprised of a colorant portion
consisting essentially of, by weight percent:
Ingredient Approximate Wt.%
Fez03 (total iron) about 0.5 - 0. 8%
FeO 0.1 - 0.2501
Er2O3 " 0.5 - 3. 0%
Ti02 " 0 - 1.0%
wherein the glass when measured at a nominal thickness of
about lmm - 6mm, and preferably about 3mm - 4mm (e.g. at
3.2mm and 4mm) has a dominant wavelength of from about
435nm to less than about 570nm and an excitation purity of
less than about 4.5%.
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In achieving (making) the above-described glasses
having the aforesaid unique colorant portion it is
preferred to include within the batch ingredients, and thus
during glass formation, a reducing agent of one or more
ingredients. In the practice of certain embodiments herein
the reducing agent is comprised of (by weight of the batch)
about 0.01 - 0.3 wt.% of silicon monoxide (Si0) and about
0 - 0.12 wt.% of metallic silicon (Si). In other
embodiments the reducing agent may be selected from one or
more conventional glass melt reducers such as sucrose, tin,
carbon, or the like.
In this respect, it was heretofore known, as reported
in U.S. Patent No. 5,569,630 (issued to two of the
inventors hereto) to use SiO as a reducing agent for the
purpose of reducing cerium and obtaining a colorless W
absorbing glass which was free of iron. In the present
invention, the combination of two lower valency forms of
silicon; namely, one agent (optional) in the form of
metallic silicon (Si ) powder, and the other, (Si2') in the
form of silicon monoxide (SiO), is utilized for the purpose
of reducing the ferric ion to the ferrous ion, thereby
obtaining a true "grey" glass with the requisite low IR
transmittance as well as low UV and high visible
transmittances, but without the necessity of the use of
cerium. Indeed, the preferred glasses of this invention
are free of any cerium (except perhaps for an inadvertent
trace amount in some instances). A distinct advantage of
this combination of Si/SiO as the reducing agent is that
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during glass melting both agents are converted into Si02,
i.e. the main component in the preferred silicate glass
matrices employed herein, without the need to add any
dopant or other residue to the glass.
In this respect, certain unique glass compositions as
contemplated by this invention comprise by weight percent:
Ingredient Wt. %
Si02 about 65 - 75
Na20 " 10 - 15
CaO " 1.5 - 15
Mg0 " 0 - 10
A1203 " 0 - 3
KZ0 " 0.1 - 1
SO3 0.1 - 0.3
Ti02 " 0 - 1.0
Fe203 " 0.50 - 0.80
FeO " 0.10 - 0.25
Er203 " 0.50 - 3.0
B203 " 0 - 12.0
In such compositions, it is preferred that they be
substantially free of one or more of Ce, Co, Se and Ni.
Most preferably the compositions are substantially free of
all of these elements. By the term "substantially free" is
meant that such an element does not exist in an amount
greater than a "trace amount" (i.e.usually as an impurity)
and is not purposely added to the mix. For the purposes of
this invention the approximate upper limit for each element
is as follows and below which the element is generally
considered to be present only in a "trace amount". Most
preferably, of course, the glass is entirely free of any
measurable amount of such elements:
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Element Wt. of Glass ("trace amount")
cerium less than about 0.0020%
cobalt " " " 0.0003%
nickel 0.0005%
selenium 0.0003%
In such instances, where these limits are not exceeded, it
may be said that such an element has no significant affect
upon the relevant solar management properties of the glass,
which, therefore, may be considered the true meaning of the
term "trace amount" as used herein.
The term "consisting essentially of" is used herein,
in its conventional way, to define the essential
ingredients while eliminating from use above a trace
amount, other colorants as described above (e.g. Co, Se,
Ce, Ni) which would significantly affect the solar
management properties of the glass if present.
While not essential to the practice of this invention,
in theory this invention may be said to achieve its true
"grey" color by recognizing (and utilizing) the known
principle of color formation that an achromatic (grey)
glass can be obtained by the interference of only two
colors, blue and pink, which if properly done, is more
appealing aesthetically (as a true "grey" color) than the
so-called "grey" colors heretofore achieved with
combinations of colorants such as Se, Co, and Ni in
combination with the background of blue color given by the
ferrous ion in the glass. In the present invention, the
very pure hue of light blue (needed for the creation of
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true "grey") is obtained in the glass by the appropriate
reduction of Fea03 to FeO (the IR absorber). This is
accomplished by a properly balanced combination or amount
of Si (optional) and SiO followed by the achromatization
(i.e. "physical bleaching") to a true grey color as defined
herein, brought about by the use of erbium oxide which
provides the true pink color to create the requisite
interference, resulting in the aesthetically pleasing grey
color of the glass.
Further slight color correction and, if desired,
further W absorption may be achieved by the addition of
titania, As noted above, Ti02 is an optional colorant and
thus its amount of about 0.0% - 1.0% is included in this
term to demonstrate that Ti02 is contemplated as an
affirmative colorant which optionally may be used above a
trace amount.
The preferred glasses according to this invention
generally exhibit, in combination, the following
characteristics as measured at their intended nominal
thickness:
a) a true "grey" color as defined above;
b) a high transmittance of visible light, with
an Lta usually equal to or greater than
about 70%;
c) a low IR transmittance less than about 37%
and preferably less than about 28%;
d) a low UV transmittance less than about 42%
and preferably less than about 38%; and
e) a low total solar transmittance less than
about 47%.
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In the aforesaid U.S. Patent No. 5,569,630 there is
additionally disclosed the technique of using a multiple
prebatch approach which employs the matrix components in
one prebatch mix and a separate prebatch mix of CeO2 and the
reducing agent. In yet another aspect of this invention,
a unique method of making the glasses of this invention has
been discovered which draws upon the teachings in U.S.
Patent No. 5,569,630 to help achieve enhancement of such
characteristics as reproducibility, optimized color, and
further improved UV and IR transmittances. For example, by
the use of such a method it has been found that the
reproducible nature of the solar management properties
achieved are optimized over ordinary techniques of mixing
all ingredients together in a single batch and, thereafter,
simply melting the batch to form a glass. Generally
speaking, these unique methods for making the glasses of
this invention, as above-described, comprise the steps of:
a) forming at least two separate prebatch mixes
which when mixed together form an overall batch
mixture comprising:
Ingredient
sand
iron oxide
erbium oxide
metallic Si
Si0 (silicon monoxide)
wherein the first prebatch mix comprises (and preferably
consists essentially of):
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Ingredient
iron oxide
metallic Si
SiO (silicon monoxide)
sand
and wherein any remaining prebatch mix or mixes include the
remaining ingredients in the overall batch mixture,
b) mixing the first prebatch mix ingredients
together separately from said remaining prebatch mix
ingredients to form the first prebatch mix,
c) mixing the remaining ingredients so as to
form at least one other separate prebatch mix,
thereafter,
d) mixing the prebatch mixes together to form
the overall batch mixture,
e) melting the overall batch mixture to form a
glass therefrom, and thereafter,
f) forming the glass into the glass article.
This invention will now be described with respect to
certain embodiments thereof, wherein:
IN THE DRAWINGS
Figure 1 is a side plan view of an automobile having
windows and a windshield employing the glasses of this
invention.
Figure 2 is a front plan view of a dwelling having an
architectural window made of the glasses of this invention.
Figure 3 is a perspective view of eyeglasses employing
glass lenses according to this invention.
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DETAILED DESCRIPTION
With reference to Figures 1-3 and as stated above,
while the glasses of this invention find unique application
in the automotive industry, they may also be used as flat
glass for the architectural market for both single sheet
windows and dual pane windows known as I.G. units. They
may also be used as eyeglass lenses. Thus, in Figure 1,
windshield W, front side windows F and rear side windows R
are illustrated for areas of use for the glasses of this
invention. Rear windows (sometimes called "backlights")
are also applicable, but are not shown for convenience. In
Figure 2 a typical house H is schematically shown with a
conventional window P having a glass sheet or sheets (when
an I.G: unit) formed of a glass according to this
invention. In Figure 3, eyeglasses E are provided with a
pair of lenses L made of a glass according to this
invention. In general, then, the glasses of this invention
find utility wherever truly "grey" glasses having low UV
and IR transmittances, as usually high LTa's, are desired
or required.
The preferred glasses for use in this invention employ
conventional soda-lime-silica flat glass as their base
composition, to which is then added certain ingredients to
make up a unique colorant portion. Of particular utility,
in this respect, are the various soda-lime-silica glasses
used in making glass sheets by the float process and
generally represented, conventionally, on a weight percent
basis, as comprised of the following basic ingredients:
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Ingredient Wt. %
Si02 68 - 75
Na20 10 - 18
CaO 5 - 15
MgO 0 - 5
A1203 0 - 5
K20 0 - 5
Other minor ingredients, including various conventional and
refining aids, such as SO31 may also be included. In the
past, furthermore, it has been known to optionally include
small amounts of Ba0 and B203. Preferably, the glasses
herein include by weight about 10-15% Na20 and 6-12% CaO.
Prior to this invention one of the inventors hereto
discovered and put into commercial practice the finding
that by using a unique amount of B203 in combination with
iron as a principal constituent in a colorant portion of a
glass, B203 synergistically modified the absorption power of
the ferrous and ferric iron, thereby achieving lower levels
of UV, T. and IR transmittances than would otherwise be
expected from such a relatively low amount of iron. This
synergism is employed in certain embodiments of this
invention as an enhancing factor to UV, IR and T.
transmittances in order to minimize these transmittances
without the use of cerium oxide or other known UV or IR
absorbers. In certain other embodiments, small amounts of
Ti0Z are optionally employed to further limit UV absorption.
The glasses of this invention, as stated above,
achieve a true grey (or "neutral grey") color, as opposed
to manifesting an objectionable "bronze", "blue grey" or
"green grey" color. Such a true "grey" color is best
defined, as aforesaid, by referring to the two
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characteristics of: (1) "dominant wavelength", and (2)
"excitation purity." Also complementing this definition is
reference to the aforesaid CIE LAB coordinates [Ill. C 2
observer] According, then, to this invention, the glasses
herein are true "grey" glasses because they have a dominant
wavelength of from about 435nm to less than about 570nm,
and most preferably between about 480nm - 550nm; coupled
with an excitation purity less than about 4.5% and
preferably from about 0.2% to about 4.5%. Such glasses
then will preferably also include the following CIE LAB
color coordinates [Ill. C 2 observer] when measured at a
nominal thickness of from about lmm - 6mm (and preferably
for most uses, at about 3mm - 4mm):
L* about 86 - 91
a* about -2.4 to +1.6
b* about -5.0 to +2Ø
Most preferably the CIE LAB color coordinates [Ill. C 2
observer] as measured at a nominal thickness of 3mm - 4mm
are:
L* about 87 - 89
a* about -0.5 to +1.0
b* about -3.0 to -1Ø
When used in the automotive market for windows and/or
windshields that must conform to certain minimal visible
light transmission properties (i.e. as measure as aforesaid
as "Lta"), the glass articles of this invention will
normally have an Lta at least equal to and preferably
greater than about 70% and, in certain embodiments, greater
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than about 72%, and in still further instances, greater
than 73%.
The glasses of this invention achieve the above unique
characteristics, particularly, for example, in silicate
glasses, and more particularly in glasses of the soda-lime-
silica type as defined above, as well as in borosilicate
glasses, by the use of a unique colorant portion which
includes a relatively high amount of iron in combination
with erbium oxide (Er203) and only, optionally, a small
amount of Ti021 to the exclusion of anything but, at most,
trace amounts of Ce, Se, Co and Ni. As such, the colorant
portions contemplated by this invention consist essentially
of, by weight percent (of the total glass composition):
Ingredient Wt.%
Fe203 (as total iron) about 0.5 - 0.8%
FeO 0.1 - 0.25%
Er203 0.5 - 3. 0%
Ti02 0.0 - 1.0%
In certain preferred embodiments, the colorant portion
of the glasses contemplated herein consist essentially of,
by weight percent (of the total glass composition):
Ingredient Wt. %
Fe203 (as total iron) about 0.6 - 0.8%
FeO " 0.16 - 0.25%
Er203 " 1.0 - 2.0%
Most preferably such a colorant portion also includes 0.1 -
0.5% Ti02. Moreover, while perhaps not classifiable as a
"colorant," nevertheless, in certain preferred embodiments
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the glasses will also include about 0.25 - 2.0 weight %
B203, and preferably about 0.25 - 1.0% weight % B2031 thereby
achieving the heretofore known synergistic enhancing effect
discussed above, but without adversely affecting color.
Certain preferred glass compositions of this invention
are generally classifiable as soda-lime-silica glasses, and
in certain preferred embodiments include by weight percent
about 10-15% Na20 and about 6-12% CaO. Still further
embodiments include high levels of B203 up to about 12% by
weight, and such glasses are then properly referred to as
being in the borosilicate family of glasses.
Still further preferred glass compositions of this
invention generally consist essentially of, by weight
percent:
Ingredient Weight %
Si0z about 65 - 75
Na20 10 - 15
CaO " 1.5 - 15
Mg0 0 - 10
A1203 0 - 3
KZ0 " 0.1 - 1
SO3 " 0.15 - 0.25
Ti02 0 - 1.0
Fe203 " 0.50 - 0.80
FeO " 0.10 - 0.25
Er203 0.50 - 3.0
B203 0 - 12.0
The glasses of this invention may be made from
standard batch ingredients using well known glass melting
and refining techniques once given the above final glass
analysis. For example, if a single, conventional batch
technique for melting is to be used, a typical batch
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example would be as follows, based upon a total of 100
parts by weight:
Batch Ingredient Parts by Wt.
sand about 70-73
soda ash " 20-26
dolomite " 16-19
limestone " 5.5-6.8
boric acid " 0.5-21
salt cake 0.2-0.7
rouge ( Fe203 ) " 0. 5- 0. 8
titania 0.1-1.0
erbium oxide 0.5-3.0
Si (metal) " 0.01-0.12
Si0 " 0.02-0.3
As discussed briefly above, while conventional single
batch melting techniques may be employed here, it is a
unique finding, and thus an additional part of this
invention, drawing upon the teachings in U.S. Patent No.
5,569,630, that if certain multiple, prebatch mixing of
selected ingredients is accomplished to make up separate
"prebatch mixes", followed thereafter by admixing together
these prebatch mixes to make up the final "overall batch
mixture," certain quality enhancing characteristics in the
final glass are achieved, principally in the ability to
more precisely obtain in repeatable batches the optimal end
result (characteristics) sought to be achieved, as well as
enhanced solar management properties. In short, by this
prebatch mix technique employing at least two prebatches of
selected ingredients, reproducibility of optimized (i.e.
maximized, or more precise) color, UV, IR, and LTa
characteristics are achieved.
In this respect, one of the prebatch mixes should be
made up of the iron-containing ingredient (e.g. rouge)
CA 02302560 2000-03-22
along with SiO (silicon monoxide) and optionally, metallic
Si (i.e. the reducing agents), and preferably some of the
sand. In preferred embodiments the total amount of the
iron (e.g. rouge), metallic Si, and SiO are used in this
first prebatch mix with a small amount of sand and are
thoroughly mixed together separately from the remaining
batch ingredients. It is preferred that, for example, on
the basis of a total of 70-73 parts of sand by weight per
hundred in the overall batch, only about 5-13 parts of sand
is used in this first prebatch mix.
The remaining batch ingredients can then be made up by
admixing them in another separate prebatch mix or into two
or more prebatch mixes before admixing them with the iron
and reducing agent-containing first prebatch mix. In
certain embodiments of this invention the remaining
ingredients are formed into two additional prebatch mixes.
The first additional prebatch mix (i.e. the second prebatch
mix) is made up of a portion of the soda ash, and all the
titania (if used) and the erbium oxide. The second
additional prebatch mix (i.e. the third prebatch mix) is
then made up of the remaining ingredients which thus
normally includes the rest of the sand (e.g. 60-65 parts
and preferably about 61.5 parts, per hundred) and soda ash,
and all of the dolomite, limestone, boric acid and salt
cake to be used in the final batch.
After each separate prebatch mix is thoroughly
separately mixed, to form a substantially homogenous
powdered admixture, the two or more prebatch mixes are then
21
CA 02302560 2000-03-22
thoroughly mixed together to form the overall (or final)
batch mixture. Conventional melting and refining
techniques are then used to form a molten glass from which
flat sheet glass or other articles may be formed.
It has been found that the use of at least two
prebatch mixes, wherein the iron is isolated with the
silicon monoxide (SiO) and metallic Si (if used), produces
glasses of a much more predictable and often optimized
nature as far as their color and other solar management
properties go.
While not essential to the practice of this invention,
it may be theorized that this multi-prebatch technique
procedure of isolating and thoroughly mixing the iron,
silicon monoxide and silicon metal in a separate prebatch
mix leads to the formation of aggregates, or "clusters" in
the batch, which form a"quasi -ingredient" of the batch.
This quasi-ingredient then comprises all the "participants"
( i. e. Fe2031 SiO and Si "dissolved" in a small amount of
sand) of the above-described reactions of reduction of
ferric ion to ferrous ion by the two lower valence forms of
silicon. By making up the quasi-ingredient from these
reactants, the probability of their encounter is increased,
thus increasing the completion of the chemical reactions in
the melt, and resulting in glasses of a more predictable
(reproducible) nature as far as their color and solar
management properties go. The above reactions are also
optimized in this quasi-ingredient (prebatch) approach for
22
CA 02302560 2000-03-22
the amounts of the ingredients employed, thus providing a
more effective use of SiO which is relatively expensive.
The following constitute examples of this invention:
EXAMPLES
Glass samples having the composition and properties
shown in the TABLE below were formed from the ingredients
listed in the first columns of this table, using the three
prebatch mixing technique as described above. The
ingredient listed as "Fe203" is total iron and was added as
conventional rouge to the first prebatch which also
included metallic silicon (when used), silicon monoxide,
and a portion (5-13 parts per hundred) of the total sand.
The second prebatch then included the erbium oxide, titania
(when used), and about one-third of the total soda ash
employed. The third prebatch included the remainder of the
ingredients as listed. The three prebatch mixes were then
mixed together to form the overall batch mixture.
The overall batch mixture was then melted in an
electric furnace in a conventional crucible at a
temperature in the range between 1480 and 1520 C. The
molten glass was then cast into molds for measurement
sampling (e.g. 2" diameter buttons), annealed at 620 C. for
1/2 hour and cooled to room temperature. The cooled glass
was polished to prepare either 4mm or 3.2mm thick specimens
which were then measured using conventional practices as
described above.
23
CA 02302560 2000-03-22
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24
CA 02302560 2000-03-22
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CA 02302560 2000-03-22
Once given the above disclosure many other features,
modifications and improvements will become apparent to the
skilled artisan. Such features, modifications and
improvements are therefore considered to be a part of this
invention, the scope of which is to be determined by the
following claims:
26
